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MA Pointer, MS Freedman, DM Hunt; Molecular Characterisation of the Visual Pigments in the Deep-sea Scopelarchid, Scopelarchus analis . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1372.
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Purpose: Blue-shifted rod opsins have been identified in many species of deep-sea fish and has become a classic example of adaptive evolution. To date, however, no cone opsin gene sequences have been isolated from a deep-sea species. The pearleye fish, Scopelarchus analis, matures at depths around 200m and then descends to 1000m once adult. This species possesses tubular eyes with a main retina subserving the dorsal field and containing two pigments with λmax values at 445 and 505 nm, and an accessory retina subserving the lateral field and containing a 479 nm pigment. Our aim was to investigate the nature of the three pigments, and determine whether solely rod opsins, or if one or more cone opsins, are expressed in the retinas of Scopelarchus analis. Methods: Southern blotting has been used to identify the opsin genes present in the genome of S. analis. Opsin sequences have been PCR amplified from genomic and retinal cDNA using degenerate teleost opsin primers, and the sequences have been extended by genomic walking and 3' RACE. Results: The opsin genes that underlie the three visual pigments have been cloned and sequenced and candidate tuning sites for the spectral shifts between pigments are identified. Conclusion: The gene sequences of the opsin genes in S. analis provide an evolutionary explanation for the multiple pigments present in this deep-sea species. These data are consistent with adaptation to differing photic environments during the lifecycle.
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